Stock pusher

ABSTRACT

This disclosure relates to a stock pusher for use in automatic screw machines or the like and includes a urethane rubber body having a passageway therethrough for grippingly engaging the stock to be pushed. The urethane body may be either permanently or removably secured in the pusher shell at the end of the stock feed tube.

United States Patent Lynn [ 1 Feb. 8, 1972 [54] STOCK PUSHER [21 Appl.No.: 19,818

[52] US. Cl. ..226/158, 279/1 Q [5!] Int. ..B65h 17/34 3,272,447 9/ 1966 Ewing .279]! Q 3,404,822 10/1968 Green 2,426,200 3/1947 Green..279/4 l X Primary Examiner-Allen N. Knowles Attorney-Burton and ParkerABSTRACT This disclosure relates to a stock pusher for usein automaticscrew machines or the like and includes a urethane rubber [5k] FieldulSearc-hmv ...226/158, 167; 279/] Q, 41,

279/46 body having a passageway therethrough for gnppmgly engaging thestock to be pushed. The urethane body may be either I 56' ReferencesCited permanently or removably secured in the pusher shell at the end ofthe stock feed tube. UNITED STATES PATENTS 7 Claims, 10 Drawing F igures3,549,072 12/1970 Kinori ..22 6/ 167 2 4 I Z4 Z6 7 8 W ,az I 3' \5 i 3 jv a4 I PATENIEIJ rm amz SHEET 1 OF 3 INVENTOR 6/4 5547 7.- zro/v BYATTOR NEYS PATENTED FEB 8m 3, 40 4 2 INVENTOR ATTORNEYS STOCK PUSHIERBACKGROUND OF THE INVENTION This invention relates to stock pushers suchas are used in automatic screw machines or the like.

Over the years stock pushers for automatic screw machines have generallybeen of three types. First, there is the pusher utilizing a plurality ofresistingly expahsible and contractable steel fingers or pads betweenwhich the stock is fed and which grips the stock to push it. The stockengaging surfaces may be of hardened steel. A second-type pusherutilizes fingers made of a softer metal such as bronze or brass. A thirdtype has stock engaging portions made of natural or neoprene rubber. Inthe case of the first type the steel fingers or pads, though having along life, tend to scratch the stock and leave undesirable scratch markson the finished product. The second type though not giving rise to themarring of the stock, generally has a relatively short life. The thirdtype does not wear well and therefore has a short life. Much time iswasted by the machine operator in attempting to prevent scratching ofthe stock by the steel pushers, and the frequent breakage or rapid wearofthe brass or bronze pushers necessitate frequent shutdowns of themachines and replacement. With the natural rubber or neoprene pushersslippage between the pusher and the stock often result in unsatisfactorymachine operation. As a consequence there has been a long felt need inindustry for a stock pusher that will alleviate the problems of theprior art pushers.

Among patents relating to stock pushers the following are of interestshowing the state of the art:

SUMMARY OF THE INVENTION The principal object of this invention is theprovisions of a stock pusher which has a long life, will not mar thestock, will maintain a good grip on the stock throughout its useful lifewithout undesirable slippage, and will allow insertion of the bar stockthereinto without internally cutting or tearing the pusher.

Other objects include the provision of a pusher which will centralizethe bar stock so that it will be concentric with the axis of themachining operations, will help reduce vibration of the bar stockthereby improving surface finish on the stock at the machining area,will reduce chatter of the stock during machining which sometimes occurswith the present commercially available pushers, will allow a machinehaving a positive cam stroke feed to use a maximum amount of the barstock without imposing undue strain on the stock-feeding mechanism, maybe used in existing automatic screw machines and the like withoutnecessitating any changes therein, which is of such design that thepusher may be readily removed and replaced by another of the same or adifferent size, and finally which is of reduced cost over the existingcommercially available pushers.

l have discovered that if the pusher is made in the form of a tubularblock of urethane rubber having the characteristics hereinafterdescribed, that it will not only satisfactorily grip the stock eventhough the latten is oiled and/or covered with corrosion-resistantcoating, but it will stand up for extended periods of use, will not marthe stock, and in addition, one pusher will accommodate different sizesand shapes of stock. In one test 50,000 screw machine parts were made ina screw machine provided with this improved urethane rubber pusher, andwhen such production run was completed and the pusher examined, it wasfound to be substantially in as good condition as when originallyinstalled, and capable of continued satisfactory use for many morethousand operations in the screw machine.

Urethane rubber has been commercially available since about 1950, andwas known for many years prior to that. but so far as I am aware no onehas suggested that it be used for a stock pusher. At least twocharacteristics of urethane seemingly argue against its usage: First,urethane has a lower coefficient of friction than either natural rubberor neoprene, both of which tend to slip, particularly on oily bar stock,and therefore to use urethane would appear illogical; Second, urethaneof a hardness suitable for use as a pusher has a much greater tendencyto take a permanent set than natural rubber or neoprene, thereforereducing its grip on the stock and militating against the selection ofurethane.

Contrary to the foregoing apparent drawbacks of urethane. I have foundthat if it is so shaped as to minimize its objectionable characteristicsand compounded to emphasize certain attainable characteristics, a pushercan be thus provided meeting the aforementioned objects and ofsurprisingly long life.

In the drawings FIG. I is a side elevation partly in section through thespindle assembly of a typical automatic screw machine, such as aGreenlee machine manufactured by Greenlee Brothers & Co. and describedin a brochure of such company published July 1949, and showing myimproved pusher mounted therein;

FIG. 2 is a side elevation of the collet lever assembly for the spindleof FIG. 1;

FIG. 3 is a cross-sectional view through a first form of pusher formounting on the end of the feed tube of the spindle assembly showing oneform of the pusher body, with a length of bar stock shown in phantomoutline extending through the pusher;

FIG. 4 is a cross-sectional view taken on the line 4-4 of FIG. 3 andshowing in cross section a piece of bar stock in the pusher;

FIG. 5 is a cross-sectional view through a portion of a second form ofpusher;

FIG. 6 is a cross-sectional view through the modified form of pushershown in FIG. 5 taken substantially on a line 66;

FIG. 7 is a cross-sectional view through a third form of the pusher;

FIG. 8 is a cross-sectional view through the pusher of FIG. 7 takensubstantially on the line 88;

FIG. 9 is a cross-sectional view through a fourth form of pusher; and

FIG. 10 is a cross-sectional view of the pusher of FIG. 9 but with adifferent form of connection of the pusher shell to the shell holder.

To provide certain background and environmental information I have shownin FIGS. 1 and 2 a spindle assembly of a typical automatic screwmachine, such as a Greenlee machine. There are a number of such spindleassemblies in a screw machine each adapted to support and automaticallyfeed stock to and hold it at a plurality of work stations. The spindleassemblies may be part of a turret which rotates all of the assembliesin a step-by-step motion from one work station to the next, or in otherforms of screw machines the spindle assemblies may be rotationallystationary and the tools to perform the work may be mounted in arotating turret. In any event the stock 5, which typically is in theform of a long bar or rod, either of polygonal or cylindricalconfiguration, is fed axially by the assembly into a working positionS-I and for this purpose is generally received through a reciprocablestock feed tube 20 which supports the stock. On the end of the tube is apusher P which grips the stock and pushes it into the work station. Thepusher reciprocates on the stock from a retracted position to anextended position, the latter being shown in FIG. 1. In the retractedposition it engages the stock for movement to the extended position. Inthe extended position the stock is at the work-performing position. Someform of stop means, schematically indicated at 22, is provided forlimiting the amount that the stock can project beyond the pusher.

In FIG. I the pusher P is mounted on the end of the stock feed tube, thefeed tube being interiorly threaded to receive exterior threads 24' onthe pusher shell 26. In FIG. 3 the pusher shell is an integral memberwhile in FIGS. 9 and 10 the shell comprises a shell holder 26' and 26"respectively, and a cylindrical tube 28 or 28' either exteriorlythreaded to be received in threaded engagement within the holder 26 asat 30, or interiorly threaded to be threadedly received over the shellholder as at 32 in FIG. 10. The feed tube is reciprocated by a collar 34surrounding the tube and shifted by a shoe assembly 36 supported bylinks 38 and engaging a cam track 40 in a drum 42 as shown in FIGS. 1and 2. The collar is held against 'axialshifting relative to the tube bya nut 44 and a shoulder 46 of the tube.

The bar stock S is held in the work-performing position by a collet Creceived in and riding the inside of a collet closing sleeve 48 securedon the end of a collet tube 50 supported within the spindle 52. A colletlever body 54 carrying springloaded collet levers 56 is mounted on thespindle with the levers overhanging the opposite end of the collet tubefrom the collet. and operable, when in the position shown in FIG. I, tolock the collet on the bar stock S. A collet operating shoe assembly 58supported on links 60 and riding a cam track 62 in the drum 42, has aportion 58' engaged in a groove in a collet spool 64 axially shiftableon the spindle to actuate the collet levers 56. When the spool isshifted to the right the levers 56 pivot to release the collet tubepermitting the collet to open, and when the spool shifts to the positionshown the levers are returned to force the collet to grip the bar stock.The spindle assembly is rotated by a gear 66 meshing with a gear train(not shown) in the screw machine. The presence and operation of otherportions of the screw machine and spindle assembly will be apparent tothose skilled in the art and need not be described.

Assuming the work has been performed on the projecting end of the barstock and the end cutoff so that it is desired to feed the bar to theright to project the newly cut end into a work-performing position, thefollowing sequence occurs. The drum is rotated to cause the shoeassembly 36 to shift to the left carrying with it the feed tube 20 andpusher I, while the collet C remains locked on the bar stock. When thepusher is thus retracted continued rotation of the drum 42 causes thecollet operating shoe assembly to shift spool 64 to the right unlockingthe levers 56 and in turn the collet C from the bar stock. Continuedrotation of drum 42 then causes the shoe assembly 36 to shift to theright thereby correspondingly shifting the feed tube and pusher. As thepusher moves to the right during its feed stroke it draws the bar stockS with it moving the stock against the stop 22. Continued rotation ofdrum 42 now shifts spool 64 to the left actuating the levers 56 to lockthe collet upon the bar stock and the stock is now ready for thework-performing operation on its projecting end 8-1.

In order to load a fresh length of bar stock in the spindle assembly,the operator inserts the end of the stock at nut 44 and pushes it downto and through the pusher P and into the collet C. Unless the end of thestock has been beveled prior to insert ing it in the feed tube, andoften it has not been, it is apparent that the relatively sharp end ofthe stock may tend to damage the pusher P as it passes therethrough.Also it will be noted that during retraction of the pusher it slides onthe bar stock and that during extension it must grip the stocksufficiently tightly so as to shift the stock to its extendedwork-performing position bringing the stock up against stop 22. Duringthis latter movement if the bar stock is carried sharply against thestop and the pusher does not exert enough holding force on the stock dueto wear or expansion of the pusher there is a tendency of the stock tobounce back from the stop and thus the pusher must desirably preventsuch bounce back to ensure the full projected amount of stock isavailable for the work-performing operation. Also, it is desirable thatthe pusher project the maximum amount of stock as the bar nears the endof its useful length without at the same time damaging the pusher. Aninspection of FIG. 1 will show that the dimension A represents theshortest length of stock, and that if the tail end of the stock is sharpor somewhat deformed there would be a tendency as the pusher pushedagainst such end to damage the pusher. Yet if the maximum amount of baris to be used up the pusher must be able to push against such endwithout being damaged.

Each of the pushers shown in the drawings includes a block of urethanehaving concentric cylindrical exterior and interior surfaces, and housedin a closely fitting pusher shell with opposite ends trapped behindradially extending wall or shoulder portions and either the exterior orinterior of the block or the shell is relieved to allow displacement ofthe urethane as the bar stock is inserted through the bore of the blockand during relative movement of the block on the bar stock. In addition,opposite ends of the bore are chamfered to facilitate insertion of theend of bar stock through the pusher and prevent gouging and tearing outof portions of the block during insertion and as the last of the stockis used up.

Referring to FIG. 3, the block 70 of urethane rubber is removablyreceived in a counterbore 72 in the shell with a pair of flat washers 74and 76 overlying the axially opposite ends of the block, and a snap ring78 received in a suitably provided groove in the shell retains the blockagainst dislodgement. The exterior wall 80 of the block is cylindricaland is a slip fit within the counterbore. The latter has a plurality ofequidistantly spaced apertures 82, four in this instance being provided,which will allow the urethane to be laterally displaced as the end ofthe bar stock or workpiece S is inserted through the bore 84 of theblock. The bore is also cylindrical and will accept either acylindricalor polygonal-shaped length of stock, such as shown in FIGS.4, 6 and 8 at S. The diameter of the bore 84 should be such that theblock tightly grips the bar stock. Because the bar will causedisplacement of the urethane, some of the urethane will enter theapertures 82 as at 86 in FIG. 4 where the displacement has beenexaggerated for purposes of illustration. Both the exteriorconfiguration of the bar stock as well as its outside dimension may varyand still be usable in a given pusher as long as a tight grip of thestock. is achieved. The washers 74 and 76 will resist elongation of theblock under the radial outward compression of the stock against theblock.

The embodiment of FIG. 5 is similar to FIG. 3 except the pusher shell 88is not provided with the apertures 82 and to' allow for displacement ofthe urethane upon insertion of the bar stock the exterior of the blockis provided with a plurality of equidistantly arranged axially extendinggrooves 90. The embodiment of FIG. 7 differs from that of FIG. 5 only inthat the grooves are in the wall of the bore 92 as at 94 and theurethane can be displaced into such grooves. In both embodiments thegrooves are relatively shallow.

The embodiments of FIGS. 9 and 10 are identical insofar as the urethaneblock is concerned. The block 96 has a very smooth and gradual taper 98at the stock-entering end to guide the end of the bar stock into thebore and the shell is provided at the opposite end with a plurality ofequidistantly spaced apertures 100 to allow for displacement of theurethane as in the FIG. 4 embodiment. In both embodiments the urethaneis retained in place by adhesive securement or bonding to the interiorof the shell. The end of the shell opposite the threads is inturned at102 to overlie the adjacent end of the urethane block to assist inretaining the block in the shell. The apertures 100 both in theembodiments of FIGS. 9 and 10 as well as FIG. 3 allow displacement ofthe urethane as the end of the stock approaches the end of the blockadjacent the apertures such that the tendency of the end of the stock totear out chunks of the block at such end is obviated.

The embodiments of FIGS. 9 and 10 contemplate that when the urethaneblock has worn out to the point where it no longer is capable ofrendering satisfactory service, the shell portion 28 (FIG. 9) or 28(FIG. 10) may be unscrewed from the portion 26' or 26" respectively anddiscarded, and a replacement shell portion threadedly connected to thesupporting portions 26' and 26". In this fashion replacement cost isminimized.

In the embodiments of FIGS. 3, 5 and 7 when the urethane blocks haveworn sufficiently so that they cannot render further satisfactoryservice, the snapring 78 shown in FIG. 3 and the corresponding rings 78'and 78" of FIGS. 5 and 7 are removed and the urethane blocks withdrawnand replacement blocks inserted followed by installation of thesnaprings.

As a result of extensive tests I have determined that there are threephysical properties of the urethane which are critical and must be metin order to provide a satisfactory pusher. The first of these is thetear strength of the urethane; the second is its compression set; thethird is its compression modulus. The pusher should have good tearstrength characteristics to resist gouging or tearing by rough or sharpedges or burrs on the bar stock. This is particularly important when theend of the bar stock is initially forced through the passageway of thepusher. My testing of the urethane pusher has indicated that the tearstrength should be at least 200 pounds per linear inch, and preferablyabout 500-600 pounds per linear inch, based on either ASTM D-470 or theInstron split tear test criteria referred to in a publication of theElastomer Chemicals Department of E. I. du Pont de Nemours and Co. ofWilmington, Delaware, entitled Tear Strength of Adiprene L Compounds,and dated Aug. 6, 1962.

With regard to compression set, the testing indicated that when urethanerubber pushers failed during testing it was not because of abrasivewear, which was what I had anticipated, though some wear did occur, butrather because the urethane took a permanent set. I have found that arelatively low compression set is desirable, preferably lying between20-30 percent, in general the lower the better, with the maximum upperlimit being 50 percent and the lowest 10 percent, as measured by theASTM standards using the constant deflection test ofmethod B.

With regard to compression modulus, namely the amount of force,expressed in pounds per square inch, required to compress a sample agiven percentage of its original height, I have found such should berelatively high and not less than 1,250 p.s.i. and preferably lying inthe range of 2,500 to 4,500 p.s.i. at 25 percent deflection, and ingeneral the higher the better.

The following are three examples of urethane rubber pushers tested andfound to be satisfactory showing the aforementioned characteristicslying in the ranges outlined. Each of the pushers were designed tooperate in a l-inch Acme Automatic Screw Machine and acceptthree-fourths inch hexagonal bar stock. Each urethane block was placedin a tubular steel pusher shell locked in a fixed aluminum yoke on atest stand. Standard lengths of three-fourths inch hex steel barattached to a reciprocating power source were inserted through the ID.of the specimens and reciprocated therethrough. One cycle was countedfor each back and forth motion with the length of each strokeapproximately 6 /2 inches, which is about five times the average feedlength for the bulk of parts run in automatic screw machines of thissize. The strokes feed was about 3 feet per second and the samples werecontinually lubricated by a dripping oiler with clean coating oil. Thenumber of cycles to failure of the samples were counted, failure beingdetermined when the sample could be shifted axially relative to the barstock by an axial force of less than approximately 300 p.s.i. Thecharacteristics of the three urethane blocks and their cycles to failureare shown below, with 75,000 cycles considered to be the minimum forsatisfactory life.

Sample 1 had a tear strength of 350 pounds per linear inch, acompression modulus of 985 p.s.i. at 25 percent deflection and acompression set of 28 percent. In addition, this sample had a hardnessshore A of 85, a tensile strength of 6,500 p.s.i., and an elongation of660 percent. This sample failed at approximately 75,000 cycles.

Sample 2 had a split tear strength of 500 pounds per linear inch, acompression modulus of 2,500 p.s.i. at 25 percent deflection, and acompression set of 27 percent. In addition, it had a hardness shore A of92, a tensile strength of 4,500 p.s.i., and an elongation of 450percent. This sample failed at approximately 200,000 cycles.

he third sample had a split tear strength of 500 pounds per linear inch,a compression modulus of 1,100 p.s.i. at 25 percent deflection, and acompression set of 28 percent. In addition, this sample had a hardnessshore A of 90, a tensile strength of 6,500 p.s.i., and an elongation of550 percent. This sample failed at approximately 125,000 cycles.

The term urethane rubber as used herein is an elastomeric resin whichmay take the form of either a polyester cured with diamines or withpolyalcohols (Glycols). A general description of the polyester resins isto be found in U.S. Pat. Nos. 2,620,616 and 2,729,618. Another basictype of resin utilizes a polyether instead of the polyester and ageneral description thereof will be found in U.S. Pat. No. 2,929,800.

What is claimed is:

1. A tubular pusher for use with a pusher shell on a feed tube in anautomatic screw machine or the like comprising a urethane rubber body oftubular configuration adapted to be received in the shell and having anaxially extending passageway adapted to telescopically receive bar stockfor feeding the same during reciprocation of the pusher: said urethanehaving a tear strength lying in the range from 200 to 600 pounds perlinear inch, a compression set lying in the range from 10 to 50 percentand a compression modulus lying in the range from 1,250 to 4,500 p.s.i.at 25 percent deflection.

2. The invention defined by claim 1 characterized in that urethanerubber has a tear strength lying in the range from 500 to 600 pounds perlinear inch, a compression set lying in the range from 20 to 30 percentand a compression modulus lying in the range from 2,500 to 4,500 p.s.i.at 25 percent deflection.

3. A stock pusher for mounting on the end of a feed tube in an automaticscrew machine or the like, comprising: a pusher shell includingthroughout at least the major portion of its length a circumferentiallycontinuous rigid wall portion, a tubular block of urethane rubbermounted in the shell and having a bore concentric therewith and capableof elastic displacement upon insertion of a bar stock through the boreto grip the bar stock for feeding movements thereof and said urethaneblock in an axially extending surface thereof provided with a pluralityof relief areas to allow for displacement of the urethane.

4. The invention defined by claim 3, characterized in that the exteriorcylindrical surface of the urethane block is provided with said relievedareas.

5. The invention defined by claim 4 further characterized in that saidrelieved areas comprise axially extending grooves spaced apart about theperiphery of the block.

6. The invention defined by claim 3 characterized in that said relievedareas are in the wall of the bore of the block.

7. The invention defined by claim 9 further characterized in that saidrelieved areas comprise grooves extending axially of the block incircumferentially spaced relation.

2mg? UNITED STATES PATENT 0mm CERTIFICATE OF CORECEEQN Patent No. 1 1 7p Febrilry 8 1972 invent fl Gilbert '1. Lyon It is certified thaterror-appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In column 6, line 61, change 'the nnine 'rel 9' t6 -6 Signed and sealedthis 30th day (SEAL) Attest: I

EDWARD M.FLETCHER,JR. ROBERT-GOTTSGHALK- Attesting Officer'Gqmissionertaof- Patents

1. A tubular pusher for use with a pusher shell on a feed tube in anautomatic screw machine or the like comprising a urethane rubber body oftubular configuration adapted to be received in the shell and having anaxially extending passageway adapted to telescopically receive bar stockfor feeding the same during reciprocation of the pusher: said urethanehaving a tear strength lying in the range from 200 to 600 pounds perlinear inch, a compression set lying in the range from 10 to 50 percentand a compression modulus lying in the range from 1,250 to 4,500 p.s.i.at 25 percent deflection.
 2. The invention defined by claim 1characterized in that urethane rubber has a tear strength lying in therange from 500 to 600 pounds per linear inch, a compression set lying inthe range from 20 to 30 percent and a compression modulus lying in therange from 2,500 to 4,500 p.s.i. at 25 percent deflection.
 3. A stockpusher for mounting on the end of a feed tube in an automatic screwmachine or the like, comprising: a pusher shell including throughout atleast the major portion of its length a circumferentially continuousrigid wall portion, a tubular block of urethane rubber mounted in theshell and having a bore concentric therewith and capable of elasticdisplacement upon insertion of a bar stock through the bore to grip thebar stock for feeding movements thereof and said urethane block in anaxially extending surface thereof provided with a plurality of reliefareas to allow for displacement of the urethane.
 4. The inventiondefined by claim 3, characterized in that the exterior cylindricalsurface of the urethane block is provided with said relieved areas. 5.The invention defined by claim 4 further characterized in that saidrelieved areas comprise axially extending grooves spaced apart about theperiphery of the block.
 6. The invention defined by claim 3characterized in that said relieved areas are in the wall of the bore ofthe block.
 7. The invention defined by claim 6 further characterized inthat said relieved areas comprise grooves extending axially of the blockin circumferentially spaced relation.